1.Field of the Invention
The present invention relates to a level shift circuit for shifting the voltage level of a current signal.
2.Description of the Related Art
In imaging equipment such as a video camera and a digital still camera, there is a requirement for preventing a video image from becoming degraded due to the occurrence of blur in a subject image by vibration and the like, such as by hand shake, and a vibration measurement mechanism is provided. This vibration measurement mechanism detects the vibration of the imaging equipment with respect to the subject, and it is known that, in response to vibration, an optical system (lens) and the like is shift-corrected by a motor and the like (see Japanese Patent Laid-Open Publication No. Hei 07-23277 etc.).
As this motor for correction, a voice coil motor and the like are used, and to make the driving of this voice coil effective, a power source of preferably high voltage is used.
Hence, after performing the amplification of the signal for driving with an internal reference voltage, the power source voltage is level-shifted to a battery power source, and as a result the circuit and the like for outputting the signal to the voice coil is adopted as a drive circuit of the voice coil.
Further, as related literature, Japanese Patent Laid-Open Publication No. 2000-244306 can be cited.
Here, the battery power source is lowered with use. Depending on the kind of the battery, there are cases where the lowering of the voltage is considerably large. In this case, when the reference voltage internally used is made undependable on the battery power source and unalterable, the reference voltage and the battery power source are sometimes reversed.
In general, the level-shift circuit is configured such that the relation of magnitude between two power sources that are the object of conversion is fixed, and the relation is not assumed to be reversed. Hence, when the relation of two power source voltages is reversed, there is a problem that the circuit is unable to perform an expected operation.